David Papineau
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1 The Problem of Consciousness David Papineau Forthcoming in The Oxford Handbook of the Philosophy of Consciousness ed Uriah Kriegel Introduction Consciousness raises a range of philosophical questions. We can distinguish between the How? , Where? , and What? questions. First, how does consciousness relate to other features of reality? Second, where are conscious phenomena located in reality? And, third, what is the nature of consciousness? In line with much philosophical writing over the past fifty years, this chapter will focus mostly on the How? question. Towards the end I shall also say some things about the Where? question. As for the What? question, a few brief introductory remarks will have to suffice. This is not to deny that the What? question raises a range of philosophically interesting issues. There is much to ask about the nature of consciousness. Must conscious states always involve some reflective awareness of themselves? Do all conscious states have an intentional content? Must consciousness always be consciousness for some subject, and if so for what kind of subject? In what sense, if any, are the conscious experiences of a subject at a given time always unified into some whole? However, in order to keep my task manageable, I shall leave issues like these for the essays that follow in this volume. For my purposes, it will be enough if we simply characterize consciousness in the normal way, as states that are “like something” for the subjects that have them. If examples are wanted, simply reflect on the difference between having your eyes open, and enjoying a range of conscious visual experiences, and closing your eyes and eliminating those conscious experiences. Or, more generally, contrast the conscious life you enjoy when you are awake, in all its rich variety, with its complete disappearance when you are given a general anaesthetic. The Case for Physicalism Let us make a start on the How? question. How does consciousness relate to other features of reality? At first pass, it might be unclear why there is any special issue here. Why is there a puzzle about conscious states, as opposed to other kinds of states? Reality contains many different kind of things, biological, meteorological, chemical, electrical, and so on, all existing alongside each other, and all interacting casually in various ways. There seems no immediate reason why consciousness should be singled out as posing some special puzzle about its relation to the rest of reality. 2 If conscious properties did interact causally with non-conscious states, then there would indeed be no special problem about its relation to other features of reality. We could all be happy interactionists, in the style of Descartes. We could hold that conscious mind influences non-conscious matter, by controlling bodily behaviour, and similarly that matter influences mind, giving rise to sensory experiences, pains and other conscious mental states. There is a compelling argument, however, against this kind of interactionist stance. This derives from the so-called “causal closure of the physical”. The problem is that the physical realm seems causally sufficient unto itself. Physical effects always issue from physical causes. This applies to bodily movements, and the neural processes which prompt them, as much as to any other physical effects. Scientists studying neural processes take it as given that the events they observe are effects of electromagnetic and chemical causes, not of independent mental influences exerting an influence from outside the physical realm. 1 The “causal closure of the physical” thus implies that, if there is a separate realm of mental states, it cannot exert any influence on bodily behaviour or other physical processes. One possible move at this point is to continue to uphold the existence of a distinct mental realm, and accept that it indeed has no influence on the physical world. However, this “epiphenomenalist” option is not only intrinsically implausible, but faces various internal difficulties. 2 Given this, most contemporary philosophers have opted instead for some form of physicalist monism. There aren’t two separate realms, mind and matter. Rather mental states are themselves a species of physical states. You might initially think of your pains or your desires as something separate from the cerebral and other physical states that accompany them. But in truth, so the physicalist thought goes, your mental states are one and the same as those physical states. On this view, of course, there is then no difficulty about pains, desires and other mental states causally influencing bodily behaviour or other physical processes. If your conscious mental states are no different from your cerebral physical states, then they will have just the same physical effects that those physical states do. If there is such a compelling argument for a physicalist view of the mind, why hasn’t physicalism always been the dominant philosophical position, rather than only becoming so in the middle of the last century? The answer is that the causal closure of the physical wasn’t generally accepted until relatively recently. Note that the 1 Perhaps the thesis of “causal” closure is better formulated as the claim that (the chances of) all physical events are determined by prior physical events according to physical law. On some views of causation, these prior determiners do not necessarily count as causes (Woodward 2005, Menzies 2008). Still, determinational closure itself sustains an argument against metaphysically independent mental influences. I shall ignore this complication in what follows. 2 In particular, epiphenomenalism is arguably self-stultifying , in that it implies that the conscious realm has no casual impact on the views of those who believe in it (Robinson 2015 sect 2.4). 3 closure-based argument against dualism isn't just the traditional objection put to Descartes by his contemporaries, that if mind and matter are so different, it is difficult to understand how they can causally interact. Even if this was a problem in Descartes’ time, it is not clear that it greatly perturbed subsequent thinkers. Rather the problem is that modern science has definite views about the kinds of things that do affect the movement of matter, and independent mental influences are not among them. To repeat, this exclusion of independent mental causes is a relatively recent phenomenon. Through most of the modern period, science had no problem with fundamental conscious causes. Orthodox physical science, from the time of Newton through to the twentieth century, was generally open-minded about the kinds of things that could influence the movements of matter. In addition to mechanical forces of impact, and gravitational forces, it allowed distinctive chemical forces, magnetic forces, forces of cohesion, vital forces—and conscious mental forces. It was only in the middle of the twentieth century that a detailed understanding of the electro-chemical workings of neurons convinced the scientific mainstream that there is no place for sui generis mental forces. 3 It is noteworthy that all the familiar modern arguments for physicalism were developed in the middle of the twentieth century, and all appealed to some version of the causal closure of the physical. 4 The Explanatory Gap There is a huge contemporary literature on physicalist views of the mind, covering a range of questions. How exactly should we define “physical”? Can mental properties be identified with basic physical properties, or should we instead embrace some version of “non-reductive physicalism”, according to which mental properties supervene on, or are grounded in, or are otherwise constituted by basic physical properties, without being strictly identical to them? Do these non-reductionist options succeed in avoiding the epiphenomenalist threat that prompted physicalism in the first place? And so on. However, we can by-pass all these issues here. This is because any version of physicalism about conscious states seems to generate pressing philosophical problems. Despite the strength of the argument for physicalism, the equation of the lived experience of perceptions, emotions, and pains with neuronal oscillations in the brain strikes many philosophers as effectively incomprehensible. As Thomas Nagel puts it in The View from Nowhere “We have at present no conception of how a single event or thing could have both physical or phenomenological aspects, or how if it did they could be related” (p 47). Or, in the more direct words of Colin McGinn, “How can technicolour phenomenology arise from soggy grey matter?” (1991, p 1.) 3 For a more detailed account of the history of causal arguments for physicalism since the seventeenth century, see the Appendix to my Thinking about Consciousness 2002. 4 See Feigl 1958, Oppenheim and Putnam 1958, Smart, 1959, Lewis 1966, Armstrong 1968, Davidson 1970. 4 To Nagel, McGinn, and many other philosophers, the idea that conscious states are at bottom physical seems obviously problematic. This is the central problem of consciousness for contemporary philosophy. Arguments from causal closure provide compelling reasons to view conscious states as physical. But any such physicalist view of consciousness strikes many as little short of unintelligible. (Since this problem arises for all versions of physicalism, non- reductive as well as reductive, I shall often simply the exposition from now on by talking of conscious states as physical, or as identical to physical states; everything that follows will apply equally to physicalist positions that view conscious states as supervenient on, or grounded in, or constituted by, physical states.) If we are to make any progress with this central problem of consciousness, we need to articulate the nature of the resistance to physicalism illustrated by the quotations from Nagel and McGinn. One useful way to do this is to compare putative mind- brain identities with similar scientific identity claims in other areas. When we are told that common salt is NaCl, or lighting is atmospheric electrical discharge, we happily accept these claims as telling us about the underlying physical nature of these everyday phenomena.